Ribociclib plus endocrine therapy for premenopausal women with hormone-receptor-positive, advanced breast cancer (MONALEESA-7): a randomised phase 3 trial

Background In MONALEESA-2, ribociclib plus letrozole showed improved progression-free survival compared with letrozole alone as first-line treatment for postmenopausal patients with hormone receptor (HR)-positive, HER2-negative, advanced breast cancer. MONALEESA-7 aimed to assess the efficacy and safety of ribociclib plus endocrine therapy in premenopausal women with advanced, HR-positive breast cancer. Methods This phase 3, randomised, double-blind, placebo-controlled trial was done at 188 centres in 30 countries. Eligible patients were premenopausal women aged 18-59 years who had histologically or cytologically confirmed HR-positive, HER2-negative, advanced breast cancer; an Eastern Cooperative Oncology Group performance status of 0 or 1; measurable disease as per Response Evaluation Criteria in Solid Tumors version 1.1 criteria, or at least one predominantly lytic bone lesion; and had not received previous treatment with cyclin-dependent kinases 4 and 6 inhibitors. Endocrine therapy and chemotherapy in the adjuvant or neoadjuvant setting was permitted, as was up to one line of chemotherapy for advanced disease. Patients were randomly assigned (1: 1) via interactive response technology to receive oral ribociclib (600 mg/day on a 3-weeks-on, 1-week-off schedule) or matching placebo with either oral tamoxifen (20 mg daily) or a non-steroidal aromatase inhibitor (letrozole 2.5 mg or anastrozole 1 mg, both oral, daily), all with goserelin (3.6 mg administered subcutaneously on day 1 of every 28-day cycle). Patients and investigators were masked to treatment assignment. Efficacy analyses were by intention to treat, and safety was assessed in all patients who received at least one dose of any study treatment. The primary endpoint was investigator-assessed progression-free survival. MONALEESA-7 is registered with ClinicalTrials.gov, NCT02278120 and is ongoing, but no longer enrolling patients. Findings Between Dec 17, 2014, and Aug 1, 2016, 672 patients were randomly assigned: 335 to the ribociclib group and 337 to the placebo group. Per investigator's assessment, median progression-free survival was 23.8 months (95% CI 19.2-not reached) in the ribociclib group compared with 13.0 months (11.0-16.4) in the placebo group (hazard ratio 0.55, 95% CI 0.44-0.69; p